1. Field of the Invention
The present invention relates to a hydrophilicity treatment method of a silicon wafer, specifically, a method for hydrophilicity treatment of a mirror surface of a silicon wafer subjected to mirror-polishing treatment followed by rinsing treatment.
2. Description of the Related Art
In ordinary silicon semiconductor wafer producing/processing processes, a silicon wafer cut off from a silicon monocrystal ingot undergoes a lapping step and an etching step, and is then subjected to mirror-polishing by use of a polishing agent liquid for making the wafer surface flat and smooth.
Mirror-polishing of a surface is usually performed at two stages of coarse polishing and finish polishing. Finally, by the finish polishing, the micro-roughness of the surface, which is the fine surface roughness thereof, is made better and the haze thereof is removed.
The cleanness of the above-mentioned silicon wafer surface produces a direct effect onto semiconductor device property. It is known that a fall in the cleanness causes a failure of device pattern formation and produces a bad effect onto electrical characteristics of semiconductor devices, and others.
This fall in the cleanness of the wafer substrate surface is mainly caused by alien pollutants adhering onto the wafer substrate surface in individual steps for processing the wafer, examples of the pollutants including particles, metal impurities and organic materials.
For this reason, a final cleaning treatment is conducted after the mirror-polishing step in order to remove the particles and other alien pollutants that remain onto the wafer surface.
In this case, water rinsing treatment has been hitherto conducted after the mirror-polishing in order to make the finish of the final cleaning perfect and constantly give a high cleanness to the surface.
As disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-217151 (hereinafter referred to as Patent Document 1), in such water rinsing treatment, a polishing agent liquid is used to subject a wafer to polishing for finishing mirror-polishing treatment, and subsequently a rinsing liquid is supplied, instead of the above-mentioned polishing agent liquid, onto the polished wafer surface under the application of low pressure or non-pressure in order to remove the polishing agent liquid remaining onto the polished wafer surface and decrease the amount of alien substances brought together with the wafer into a final cleaning step.
After this water rinsing treatment, the wafer is transported into a cleaning device for conducting the final cleaning step while the wafer is kept wet.
Incidentally, the particles and the other pollutants can be decreased to some degree by the above-mentioned water rinsing treatment and cleaning in the cleaning device.
However, the cleaning is insufficient for higher-level wafer-surface-cleaning treatment desired at present.
In particular, the following problem arises: the polished wafer surface becomes very active (hydrophobic surface) by the mirror-polishing treatment therefor; thus, at the stage of water rinsing treatment, the polished wafer surface contacts rinsing water for the rinsing treatment or the polishing cloth, and conversely there arises a problem that particles adheres to the surface.
The particles adhering at the water rinsing treatment are very firm; thus, it is difficult to remove the particles completely even in the final cleaning treatment.
One method for countering this problem is a method of making the above-mentioned hydrophobic wafer surface hydrophilic. It is known that this method can restrain particles or metal ions from being adsorbed firmly onto the wafer surface.
Patent Document 1 discloses a technique of bringing a polishing agent liquid into contact with a wafer subjected to mirror-polishing without subjecting the wafer to any water rinsing treatment, thereby making the wafer mirror surface hydrophilic.
In this case, the polished silicon surface is certainly made hydrophilic, so as to produce an effect sufficient for restraining the adhesion of particles or metal ions.
However, at the final polishing step, the polishing agent liquid is brought into contact with the silicon surface so that colloidal silica contained in this polishing agent liquid aggregates or sticks firmly into the polishing device. Conversely, therefore, the silica causes the silicon surface to be injured when the silicon surface is polished.
The polishing agent sticking into the device induces filter-stuffing in a polishing agent liquid line or pure water line which has circulating function and is fitted to the device. As a result, there is caused a problem that troubles are made in the polishing device.
The inventors have made eager investigations on hydrophilicity treatment wherein no colloidal silica is used but advantages equivalent to those of hydrophilicity treatment using a polishing agent liquid which contains colloidal silica should be produced. As a result, the present invention has been made.